A colonoscopy is an exam that views the inside of the colon (large intestine) and rectum, using a tool called a colonoscope.

The colonoscope has a small camera attached to a flexible tube that can reach the length of the colon.

There are 4 basic tests for colon cancer: a stool test (to check for blood); sigmoidoscopy (inspection of the lower colon; colonoscopy (inspection of the entire colon); and double contrast barium enema. All 4 are effective in catching cancers in the early stages, when treatment is most beneficial.

A sample of colon tissue is obtained during a colonoscopy procedure using special instruments. The specimen is sent to the laboratory and fixed with special stains. The specimen is examined under the microscope for abnormal findings, such as cancer or inflammation.

How the Test is Performed

Colonoscopy is done most often in a procedure room at your doctor's office. It can also be done in the outpatient department of a hospital or medical center.

You will be asked to change out of your street clothes and wear a hospital gown for the procedure.

The colonoscope is gently inserted through the anus. It is carefully moved into the beginning of the large intestine. The scope is slowly advanced as far as the lowest part of the small intestine.

Air is inserted through the scope to provide a better view. Suction may be used to remove a fluid or stool.

The doctor gets a better view as the scope is moved back out. So, a more careful exam is done while the scope is being pulled back.

Tissue samples (biopsy) or polyps may be removed using tiny tools inserted through the scope. Photos may be taken using the camera at the end of the scope. If needed, procedures, such as laser therapy, are also done.

How to Prepare for the Test

Your bowel needs to be completely empty and clean for the exam. A problem in your large intestine that needs to be treated may be missed if your intestines are not cleaned out.

Your health care provider will give you the steps for cleansing your bowel. This is called bowel preparation. Steps may include:

Using enemas

Not eating solid foods for 1 to 3 days before the test

Taking laxatives

You need to drink plenty of clear liquids for 1 to 3 days before the test. Examples of clear liquids are:

Clear coffee or tea

Fat-free bouillon or broth

Gelatin

Sports drinks without added color

Strained fruit juices

Water

You will likely be told to stop taking aspirin, ibuprofen, naproxen, or other blood-thinning medicines for several days before the test. Keep taking your other medicines unless your doctor tells you otherwise.

You will need to stop taking iron pills or liquids a few days before the test, unless your provider tells you it is OK to continue. Iron can make your stool dark black. This makes it harder for the doctor to view inside your bowel.

How the Test will Feel

The medicines will make you sleepy so that you may not feel any discomfort or have any memory of the test.

You may feel pressure as the scope moves inside. You may feel brief cramping and gas pains as air is inserted or the scope advances. Passing gas is necessary and should be expected.

After the exam, you may have mild abdominal cramping and pass a lot of gas. You may also feel bloated and sick to your stomach. These soon go away.

You should be able to go home 1 hour after the test. You must plan to have someone take you home after the test, because you will be woozy and unable to drive. The providers will not let you leave until someone arrives to help you.

When you are home, follow instructions on recovering from the procedure. These may include:

Drink plenty of liquids. Eat a healthy meal to restore your energy.

You should be able to return to your regular activities the next day.

Avoid driving, operating machinery, drinking alcohol, and making important decisions for at least 24 hours after the test.